Which of the following sonobuoys provides water temperature data?

The BT sonobuoys, or "bathythermograph" sonobuoys, are specifically designed to provide water temperature data at various depths. They measure the temperature of the water column as they descend and transmit this information back to the operator. This data is essential for maritime operations, especially in anti-submarine warfare, as it helps determine sound propagation conditions underwater, which can be highly influenced by temperature gradients.

The other types of sonobuoys serve different purposes: LOFAR (Low Frequency Active) sonobuoys are primarily used for detecting submarines by emitting low-frequency sound waves, DIFAR (Directional Frequency Analysis and Recording) sonobuoys focus on detecting and determining the direction of underwater sounds, and Active sonobuoys transmit energy to elicit responses from submarines. While each of these types has its critical role in naval operations, the BT sonobuoys stand out for their specific function of measuring and reporting water temperature data.